Pipeline leakage detection method and device based on negative pressure induction and nitrogen concentration change

Abstract

The present application relates to pipeline leakage detection technical field, disclose a kind of pipeline leakage detection method based on negative pressure induction and nitrogen concentration change, double detection point is set up on negative pressure pipeline, nitrogen, oxygen, pressure and temperature and humidity sensor are respectively installed;Real-time data acquisition and carry out temperature and humidity compensation conversion dry base standard concentration;The nitrogen dry base standard concentration difference, oxygen dry base standard concentration difference and pressure difference of two detection points are calculated;Difference is compared with preset threshold respectively, and any difference is over threshold, then determine leakage.The present application also discloses a kind of pipeline leakage detection device based on negative pressure induction and nitrogen concentration change.The present application is based on negative pressure induction and nitrogen concentration change pipeline leakage detection method and device, utilize the negative pressure induction characteristics of pipeline itself, with nitrogen in air as passive tracer factor, combined with oxygen concentration difference and pressure difference linkage determination leakage and estimate gas leakage, limit condition is small, anti-interference ability is strong, can be on-line continuous operation.

Description

Technical Field

[0001] This invention relates to the field of pipeline leak detection technology, specifically to a pipeline leak detection method and device based on negative pressure induction and nitrogen concentration changes. Background Technology

[0002] In environmental protection, petrochemical, and soil remediation projects, negative pressure pipelines are widely used for the extraction and collection of waste gas and pollutants. These pipelines are mostly laid underground or in open environments; leaks will lead to reduced extraction efficiency, pollutant escape, and safety hazards. Existing leak detection methods include tracer gas detection, acoustic detection, smoke testing, and differential pressure holding methods, but these methods have the following problems: 1) The tracer gas detection method requires the injection of expensive tracer gas and replacement of the original gas in the pipeline, which results in high deployment costs and interference with the normal operation of the pipeline. Instrument detection requires manual inspection, which is difficult to cover long-distance pipelines, has blind spots, and cannot achieve real-time online monitoring. 2) Acoustic detection methods are easily affected by environmental interference such as wind noise and mechanical noise, have low sensitivity to minor leaks, and require a relatively quiet environment around the pipeline, which is difficult to meet in field conditions. 3) The smoke test method requires artificially spraying smoke at the pipe opening or joint. The number of inspection points is limited, and it cannot cover buried or remote parts. The smoke is easily affected by wind direction, which can lead to inaccurate positioning. It also cannot achieve long-term online monitoring. 4) The differential pressure maintenance method requires the pipeline to be sealed in sections and a stable differential pressure to be maintained. The operation is cumbersome and affects normal transportation. For long-distance or multi-branch pipelines, the detection efficiency is low, there are many blind spots, and it is difficult to quickly detect and locate leaks.

[0003] Chinese Patent (Publication Date: September 10, 2014, Publication No.: CN104034371A) discloses a method for measuring the air leakage rate of a sintering machine system. This method is based on the principle that N2 does not participate in the reaction during sintering and uses N2 balance for air leakage measurement. The method includes the following steps: 1) Extending the side plate of the sintering machine trolley upwards to ensure that the surface of the sintering material and the upper edge of the trolley side plate form a material-free space; 2) Measuring the air inlet velocity of the sintering material layer, and measuring the flue gas velocity, flue gas temperature, nitrogen concentration in the flue gas duct, and flue gas pressure in the flue gas duct; 3) Calculating the air leakage rate according to the measured data using the following formula. This invention can measure the air leakage rate of a sintering system relatively simply and accurately, solving the shortcomings of current measurement techniques, such as inconvenience, large errors, and the limitation that the air leakage point velocity measurement method can only measure local air leakage. However, this solution relies on the structural characteristics of the furnace body and is not suitable for rapid leakage detection in conventional closed pipeline systems.

[0004] Chinese patent (publication date: June 1, 2021, publication number: CN112880941A) discloses a method for rapid air leakage detection in underground goaf areas. This method includes: determining the release point and sampling points for air leakage detection in the goaf based on the internal structure and differential pressure test of the goaf to be tested; injecting nitrogen into the goaf at the release point, and after monitoring the flow rate and pressure of the nitrogen injection pipe to stabilize, releasing SF6 gas into the goaf from the release point and recording the release time; collecting gas samples when SF6 gas is detected at each sampling point; detecting the SF6 concentration of each gas sample using a gas chromatograph to determine the SF6 concentration in the gas samples collected at each sampling point at each sampling time; obtaining the air leakage situation of the goaf to be tested based on the shortest leakage distance between the release point and each sampling point, the release time, the SF6 concentration at each sampling point at each sampling time, the sampling time when SF6 is first detected at each sampling point, and the sampling time when the maximum SF6 concentration is detected at each sampling point, which can quickly detect the air leakage situation of the goaf to be tested. However, this scheme requires the additional injection of SF6 tracer gas, which is complex to operate, and SF6 is a greenhouse gas, which is not conducive to environmental protection applications, and is significantly different from the technical solution of this invention.

[0005] Therefore, developing a method with fewer constraints, based on the pipeline's own negative pressure and using the nitrogen composition in the air and pressure difference to determine environmental pipeline leaks and leakage amounts, has significant practical value. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the above-mentioned technologies by providing a pipeline leak detection method and device based on negative pressure induction and nitrogen concentration changes. This method utilizes the negative pressure induction characteristics of the pipeline itself, uses nitrogen in the air as a passive tracer, and combines oxygen concentration difference and pressure difference to determine the leak and estimate the leakage amount. It has few limitations, strong anti-interference ability, and can operate continuously online.

[0007] To achieve the above objectives, the pipeline leak detection method based on negative pressure induction and nitrogen concentration change designed in this invention includes the following steps: S1) On the pipeline under negative pressure during operation, a first detection point P1 and a second detection point P2 are set along the axial direction. Both detection points are equipped with nitrogen concentration sensor, oxygen concentration sensor, pressure sensor and temperature and humidity sensor. S2) Real-time acquisition of nitrogen concentration, oxygen concentration, pressure, temperature and humidity data at the first detection point P1 and the second detection point P2; calculation of water vapor partial pressure based on temperature and humidity data; conversion of the original nitrogen and oxygen concentrations into dry basis standard conditions concentrations. S3) Calculate the nitrogen dry basis standard condition concentration difference ΔN, oxygen dry basis standard condition concentration difference ΔO, and pressure difference ΔP between the first detection point P1 and the second detection point P2 at the same time. S4) The nitrogen dry-basis standard concentration difference ΔN, the oxygen dry-basis standard concentration difference ΔO, and the pressure difference ΔP are respectively compared with the preset nitrogen threshold ε. N Oxygen threshold ε O Pressure threshold ε P The comparison is performed, and if any difference exceeds the corresponding threshold, it is determined that there is a leak in the pipeline.

[0008] The core principle of this invention lies in the following: When a negative pressure pipeline ruptures, external air (containing approximately 78% nitrogen and 21% oxygen) is passively drawn downstream of the rupture point due to the pressure difference between the inside and outside of the pipeline. This results in significantly higher nitrogen and oxygen concentrations at the downstream detection point P2 compared to the upstream detection point P1, while the absolute pressure at P2 decreases. By linking the concentration and pressure differences at these two points, false alarms caused by fluctuations in a single parameter can be effectively eliminated. Nitrogen in the air is used as a natural passive tracer, eliminating the need for additional tracer gas injection. Temperature and humidity compensation converts the original measurements to dry-basis standard concentrations, eliminating the interference of environmental humidity on concentration measurements and ensuring consistency in detection under different climatic conditions.

[0009] Preferably, in step S2), the water vapor partial pressure P H2O Calculate using the following formula: P H2O =H×6.112×exp((17.62×T) / (243.12+T)) 100, where H is the relative humidity and T is the temperature.

[0010] Preferably, the converted nitrogen dry-basis standard condition concentration C std =C meas ×(P meas -P H2O ) / P std ×(T meas +273.15) / T std In the formula, C meas P represents the nitrogen concentration detected at the first detection point P1 and the second detection point P2. meas T represents the absolute pressure at the first detection point P1 and the second detection point P2. meas P represents the temperature detected at the first detection point P1 and the second detection point P2. std For standard atmospheres, T std The standard state temperature is 273.15 K. Conversion of oxygen dry basis standard condition concentration O std =O meas ×(P meas -P H2O ) / P std ×(T meas +273.15) / T std In the formula, O measis the oxygen concentration detected at the first detection point P1 and the second detection point P2, P meas is the absolute pressure at the first detection point P1 and the second detection point P2, T meas is the temperature detected at the first detection point P1 and the second detection point P2, P std is the standard atmospheric pressure, T std is the standard state temperature, with a value of 273.15K. Through temperature compensation and standard condition conversion, the influence of ambient temperature changes on the concentration measurement value is eliminated, making the detection data under different times and different climatic conditions comparable.

[0011] Preferably, after a leak is determined, the gas leakage amount is estimated based on the concentration change rates of nitrogen and oxygen and the pressure change rate in combination with a calibration coefficient.

[0012] Preferably, the formula for estimating the gas leakage amount is: Q leak =α N ×ΔN / Δt+α O ×ΔO / Δt+β×ΔP / Δt, where α N is the contribution coefficient of the change of nitrogen dry basis standard condition concentration to the gas leakage amount, α O is the contribution coefficient of the change of oxygen dry basis standard condition concentration, β is the contribution coefficient of the pressure change, Δt is the sampling interval. The contribution coefficients α N , α O , and β are obtained by performing calibration experiments under no-leakage working conditions, using the leak with a known aperture or the controllable gas leakage amount to compare and calibrate with the actually measured concentration change rate or pressure change rate. Through the three-parameter joint model, the information of the change of nitrogen dry basis standard condition concentration, the change of oxygen dry basis standard condition concentration and the pressure change can be comprehensively utilized, so as to improve the accuracy of gas leakage amount estimation.

[0013] Preferably, the gas leakage amount is classified by level to trigger on-site alarm or upload to a remote monitoring platform through a communication module, so as to realize online automatic response Preferably, a first threshold Q1 and a second threshold Q2 are set, Q1<Q2. If the gas leakage amount Q leak ≤Q1, it is determined that there is no obvious leakage; if Q1<Q leak <Q2, it is determined that there is a slight leakage; if Q leak ≥Q2, it is determined that there is a serious leakage. Through hierarchical management, the system can automatically take different response measures according to the severity of the leakage, such as issuing a warning notification when there is a slight leakage and automatically triggering an emergency shutdown valve when there is a serious leakage.

[0014] Preferably, in step S1), the nitrogen concentration sensor has a range of 0 to 10% and an accuracy of ±0.01%, the oxygen concentration sensor has a range of 0 to 5% and an accuracy of ±0.005%, the pressure sensor has a range of -10 kPa to +10 kPa and an accuracy of ±10 Pa, and the temperature and humidity sensor has a temperature range of -20℃ to +60℃ and an accuracy of ±0.5℃, and a humidity range of 0 to 100% and an accuracy of ±2%RH. By reasonably configuring the sensor accuracy, the sensitive detection requirements for minute leaks can be met.

[0015] A pipeline leak detection device based on negative pressure induction and nitrogen concentration change, used for pipeline leak detection based on negative pressure induction and nitrogen concentration change, comprising: The first detection unit and the second detection unit are respectively installed at the first detection point P1 and the second detection point P2 along the pipeline axis. Each detection unit includes a nitrogen concentration sensor, an oxygen concentration sensor, a pressure sensor and a temperature and humidity sensor. The data acquisition and preprocessing module is connected to each sensor and is used to collect nitrogen concentration, oxygen concentration, pressure, temperature and humidity data at the first detection point P1 and the second detection point P2 in real time. It calculates the water vapor partial pressure based on the temperature and humidity data and converts the original concentrations of nitrogen and oxygen into dry basis standard conditions. The difference calculation module is used to calculate the nitrogen dry basis standard condition concentration difference ΔN, the oxygen dry basis standard condition concentration difference ΔO, and the pressure difference ΔP between the first detection point P1 and the second detection point P2 at the same time. The leakage detection module is used to compare ΔN, ΔO, and ΔP with a preset nitrogen threshold ε. N Oxygen threshold ε O Pressure threshold ε P The comparison is performed, and if any difference exceeds the corresponding threshold, it is determined that there is a leak in the pipeline.

[0016] In this device, the first detection point P1 is located upstream of the pipeline near the vacuum pump outlet, and the second detection point P2 is located downstream of the contribution coefficient. When a breach occurs in the pipeline between the contribution coefficient and P2, external air enters the pipeline due to the pressure difference between the inside and outside of the pipeline. This causes the nitrogen and oxygen concentrations at P2 to increase relative to the contribution coefficient, while the absolute value of the negative pressure at P2 decreases. The difference calculation module compares the concentration difference and pressure difference between the two points in real time, and the leak detection module uses a three-parameter linkage detection strategy of nitrogen, oxygen, and pressure to effectively filter false alarms caused by occasional fluctuations in a single parameter.

[0017] Preferably, it also includes a leakage estimation module, which is used to estimate the leakage amount based on the concentration change rate and pressure change rate, combined with the contribution coefficient, after a leakage is determined.

[0018] Compared with the prior art, the present invention has the following advantages: 1. It directly utilizes approximately 78% nitrogen in the air as a natural leak indicator. When the pipeline is damaged and outside air enters, the downstream nitrogen concentration naturally increases. No tracer gas needs to be injected, which simplifies the detection process, reduces system complexity and operating costs, and is suitable for continuous operation systems in the field. 2. By simultaneously monitoring the nitrogen and oxygen concentration differences, air ingress can be accurately confirmed when both rise simultaneously, avoiding the problem of being easily disturbed by background changes when only one concentration fluctuates. Combined with pressure difference changes, the location and extent of the leak can be further verified, significantly reducing the false alarm rate. 3. By collecting temperature and humidity data in real time to calculate water vapor partial pressure, the original concentration is converted into dry basis standard concentration, which effectively eliminates the influence of environmental humidity on concentration measurement, makes the detection data under different climatic conditions comparable, and improves detection accuracy and consistency. 4. Based on the rate of change of concentration and the rate of change of pressure, the leakage volume can be estimated quickly and accurately, and the leakage level can be classified accordingly. This allows the system to automatically take graded response measures according to the severity of the leakage, thus enhancing the practicality of the project. 5. Online real-time detection with fast response: A complete leak detection and response can be completed within the sampling period, meeting the needs for rapid detection and handling of leaks in the field environment, and overcoming the shortcomings of traditional methods such as manual inspection, long detection cycle and inability to monitor online in real time. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart of the pipeline leak detection method based on negative pressure induction and nitrogen concentration change of the present invention. Figure 2 This is a schematic diagram of the pipeline leak detection device based on negative pressure induction and nitrogen concentration change according to the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be noted that the terms center, up, down, left, right, vertical, horizontal, inner, and outer, indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms first, second, and third are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] Taking the buried (PureNitrogen) negative pressure extraction pipeline network as an example, the pipeline material is carbon steel, with a diameter of 100mm and a total length of approximately 60m. Pure nitrogen gas (O2 content <0.5%) is transported inside the pipeline, and the negative pressure inside the pipeline during operation is approximately -1.5kPa. To ensure the integrity of the system, it is necessary to monitor online whether air (containing nitrogen and oxygen) leaks into the pipeline and to quantitatively assess the leakage amount.

[0024] Combination Figure 1 and Figure 2 As shown, a pipeline leak detection method based on negative pressure induction and nitrogen concentration change includes the following steps: S1) On the pipeline under negative pressure during operation, a first detection point P1 is set up along the pipeline axis at a distance of 10 m from the vacuum pump outlet, and a second detection point P2 is set up at a distance of 40 m from the vacuum pump outlet. Both detection points are equipped with nitrogen concentration sensors, oxygen concentration sensors, pressure sensors, and temperature and humidity sensors, as detailed below: Nitrogen concentration sensors C1 and C2 (range 0-10%, accuracy ±0.01%). Oxygen concentration sensors O1 and O2 (range 0-5%, accuracy ±0.005%). Pressure sensors P1g and P2g (range -10kPa to +10kPa, accuracy ±10Pa). Temperature and humidity sensors T1 / H1 and T2 / H2 (temperature range -20℃ to +60℃, accuracy ±0.5℃; humidity range 0-100%, accuracy ±2%RH); The system sampling interval Δt is set to 60s; S2) Real-time acquisition of nitrogen concentration, oxygen concentration, pressure, temperature, and humidity data at the first detection point P1 and the second detection point P2; calculation of water vapor partial pressure P based on temperature and humidity data. H2O Calculated using the following formula: P H2O =H×6.112×exp((17.62×T) / (243.12+T)) 100, In the formula, H represents relative humidity, T represents temperature, and the original concentrations of nitrogen and oxygen are converted to dry-basis standard condition concentrations: Conversion of nitrogen dry basis standard condition concentration C std =C meas ×(P meas -P H2O ) / P std ×(T meas +273.15) / T std In the formula, C meas P represents the nitrogen concentration detected at the first detection point P1 and the second detection point P2. meas T represents the absolute pressure at the first detection point P1 and the second detection point P2. meas P represents the temperature detected at the first detection point P1 and the second detection point P2. std For standard atmospheres, T std The standard state temperature is 273.15 K. Conversion of oxygen dry basis standard condition concentration O std =O meas ×(P meas -P H2O ) / P std ×(T meas +273.15) / T std In the formula, O meas P represents the oxygen concentration detected at the first detection point P1 and the second detection point P2. meas T represents the absolute pressure at the first detection point P1 and the second detection point P2. meas P represents the temperature detected at the first detection point P1 and the second detection point P2. std For standard atmospheres, T std The standard state temperature is 273.15 K. S3) Calculate the nitrogen dry basis standard condition concentration difference ΔN, oxygen dry basis standard condition concentration difference ΔO, and pressure difference ΔP between the first detection point P1 and the second detection point P2 at the same time. S4) The nitrogen dry-basis standard concentration difference ΔN, the oxygen dry-basis standard concentration difference ΔO, and the pressure difference ΔP are respectively compared with the preset nitrogen threshold ε. N =200ppm, oxygen threshold ε O=50ppm, pressure threshold ε P The values ​​are compared at 50Pa. If any difference exceeds the corresponding threshold, the pipeline is determined to be leaking.

[0025] Specifically, at the moment when the system is just started up and there is no leakage (t0=0s), each sensor collects the following data: First detection point P1: Temperature T1(0) = 20.0℃, relative humidity H1(0) = 70%, nitrogen concentration C 1_meas (0) = 1.00%, Oxygen concentration O 1_meas (0) = 0.10%, pressure P1(0) = -1500 Pa; Second detection point P2: Temperature T2(0) = 20.5℃, relative humidity H2(0) = 68%, nitrogen concentration C 2_meas (0) = 1.02%, Oxygen concentration O 2_meas (0) = 0.103%, pressure P2(0) = -1500Pa; At this time, ΔN(0)≈+0.02%(200ppm), ΔO(0)=+0.003%(30ppm), and ΔP(0)=0Pa are all within the allowable range, indicating no leakage.

[0026] At t1=60s, a micro-crack appeared in the middle section of the pipe, causing passive intake of air (78% nitrogen and 21% oxygen in the atmosphere). The collected data are as follows: First detection point P1: Temperature T1(60) = 20.1℃, relative humidity H1(60) = 71%, nitrogen concentration C1_meas(60) = 1.05%, oxygen concentration O1_meas(60) = 0.12%, pressure P1(60) = -1500Pa; Second detection point P2: Temperature T2(60) = 20.6℃, relative humidity H2(60) = 69%, nitrogen concentration C2_meas(60) = 1.50%, oxygen concentration O2_meas(60) = 0.50%, pressure P2(60) = -1400Pa.

[0027] Calculate the partial pressure of water vapor: First detection point P1: P1_ H2O =71%×6.112×exp((17.62×20.1) / (243.12+20.1)) 100 = 1691 Pa.

[0028] Second detection point P2: P2_ H2O=69%×6.112×exp((17.62×20.6) / (243.12+20.6)) 100 = 1697 Pa.

[0029] Conversion to dry-basis standard concentration: First detection point P1: Nitrogen concentration on dry basis under standard conditions: C1_ std =C1_ meas ×(P1_ meas -P1_ H2O ) / P std ×(T1_ meas +273.15) / T std =1.05%×(101325-1500-1691) / 101325×(20.1+273.15) / 273.15=10950ppm, C1_ meas The nitrogen concentration detected at the first detection point P1, P1_ meas The absolute pressure at the first detection point P1, P std T1 is the standard atmospheric pressure. meas T is the temperature detected at the first detection point P1. std The standard state temperature is 273.15 K. Oxygen dry basis standard condition concentration: O1_ std =O1_ meas ×(P1_ meas -P1_ H2O ) / P std ×(T1_ meas +273.15) / T std =0.12%×(101325-1400-1691) / 101325×(20.1+273.15) / 273.15=1250ppm, O1_ meas The oxygen concentration detected at the first detection point P1, P1_ meas The absolute pressure at the first detection point P1, P std T1 is the standard atmospheric pressure. meas T is the temperature detected at the first detection point P1. std The standard state temperature is 273.15 K. Second detection point P2: Nitrogen concentration on dry basis under standard conditions: C2_ std =C2_ meas ×(P2_ meas -P2_ H2O ) / P std×(T2_ meas +273.15) / T std =1.50%×(101325-1400-1697) / 101325×(20.6+273.15) / 273.15=15620ppm, C2_ meas The nitrogen concentration detected at the second detection point P2, P2_ meas The absolute pressure at the second detection point P2, P std T2 is the standard atmospheric pressure. meas T is the temperature detected at the second detection point P2. std The standard state temperature is 273.15 K. Oxygen dry basis standard condition concentration: O2_ std =O2_ meas ×(P2_ meas -P2_ H2O ) / P std ×(T2_ meas +273.15) / T std =0.50%×(101325-1400-1697) / 101325×(20.6+273.15) / 273.15=5210ppm,O2_ meas The oxygen concentration detected at the second detection point P2, P2_ meas The absolute pressure at the second detection point P2, P std T2 is the standard atmospheric pressure. meas T is the temperature detected at the second detection point P2. std The standard state temperature is 273.15 K. Calculate the difference: Nitrogen dry-basis standard condition concentration difference ΔN = C2_ std -C1_ std =15620-10950=4670ppm; Oxygen dry-basis standard condition concentration difference ΔO = O2_ std -O1_ std =5210-1250=3960ppm; Pressure difference ΔP = P2(60) - P1(60) = -1400 + 1500 = 100 Pa.

[0030] Compared with the preset nitrogen threshold ε N =200ppm, oxygen threshold ε O =50ppm, pressure threshold ε P By comparing the pressure to 50Pa, it was determined that there was a leak in the pipeline.

[0031] After determining a leak, the leak rate is estimated based on the concentration change rates of nitrogen and oxygen and the pressure change rate in combination with calibration coefficients, with the formula: Q leak =α N ×ΔN / Δt+α O ×ΔO / Δt+β×ΔP / Δt, where α N is the contribution coefficient of the change in the dry basis standard condition concentration of nitrogen to the leak rate, α O is the contribution coefficient of the change in the dry basis standard condition concentration of oxygen, β is the contribution coefficient of the pressure change, Δt is the sampling interval, and the contribution coefficients α N , α O , and β are obtained by performing calibration experiments under leak-free working conditions, using the leak of a known pore size or a controllable leak rate to calibrate against the actually measured concentration change rate or pressure change rate. In this embodiment: Q leak =α N ×ΔN / Δt+α O ×ΔO / Δt+β×ΔP / Δt=0.5×4670 / 1+0.8×3960 / 1+0.3×100 / 1=5533L / min.

[0032] The approximate leak flow rate at this leak point is estimated to be about 5533L / min. In this embodiment, the contribution coefficients α N =0.5L / (min·ppm), α O =0.8L / (min·ppm), β=0.3L / (min·Pa) are adopted, and the sampling section volume V≈7.85L (estimated based on a pipe length of 1m and a diameter of 100mm).

[0033] In addition, the leak rate is further classified by level to trigger on-site alarms or upload to the remote monitoring platform through the communication module to realize online automatic response. In this embodiment, a first threshold Q1=500L / min and a second threshold Q2=2000L / min are set. If the leak rate Q leak ≤Q1, it is determined that there is no obvious leak; if Q1<Q leak <Q2, it is determined as a minor leak; if Q leak ≥Q2, it is determined as a severe leak.

[0034] In this embodiment, Q leak ≥Q2, which should be determined as a severe leak. The system automatically triggers an on-site alarm, sends a notification to the on-duty personnel, and activates the emergency shut-off valve or closes the corresponding valve within 1 minute.

[0035] On-site personnel found that the sealing gasket had aged and developed cracks at the flange interface about 1m downstream of P2. After replacing the new sealing gasket and restoring the pipeline seal, the measurement was carried out again, and the measured values at this time: C1_ std=1.08%, O1_ std =0.12%, C2_ std =1.10%, O2_ std =0.13%; ΔN=20ppm<ε N ΔO = 10ppm < ε O The test results showed that the leak had disappeared and the system had returned to normal operation.

[0036] Finally, this embodiment also includes a pipeline leak detection device based on negative pressure induction and nitrogen concentration change, used for pipeline leak detection based on negative pressure induction and nitrogen concentration change, including: The first detection unit and the second detection unit are respectively installed at the first detection point P1 and the second detection point P2 along the pipeline axis. Each detection unit includes a nitrogen concentration sensor, an oxygen concentration sensor, a pressure sensor and a temperature and humidity sensor. The data acquisition and preprocessing module is connected to each sensor and is used to collect nitrogen concentration, oxygen concentration, pressure, temperature and humidity data at the first detection point P1 and the second detection point P2 in real time. It calculates the water vapor partial pressure based on the temperature and humidity data and converts the original concentrations of nitrogen and oxygen into dry basis standard conditions. The difference calculation module is used to calculate the nitrogen dry basis standard condition concentration difference ΔN, the oxygen dry basis standard condition concentration difference ΔO, and the pressure difference ΔP between the first detection point P1 and the second detection point P2 at the same time. The leakage detection module is used to compare ΔN, ΔO, and ΔP with a preset nitrogen threshold ε. N Oxygen threshold ε O Pressure threshold ε P The comparison is performed, and if any difference exceeds the corresponding threshold, it is determined that there is a leak in the pipeline.

[0037] It also includes a leakage estimation module, which estimates the leakage amount based on the rate of change of concentration and the rate of change of pressure, combined with the contribution coefficient, after a leak is detected.

[0038] In other embodiments, an output and alarm module can also be set up to classify the leakage level according to the amount of leakage, trigger an alarm, or upload the data to a remote monitoring platform through a communication module.

[0039] Finally, it should be noted that the above description is a further detailed explanation of the invention in conjunction with specific embodiments. It should not be considered that the specific implementation of the invention is limited to these descriptions. For those skilled in the art, any simple substitutions made without departing from the concept of the invention should be considered within the scope of protection of this invention. The above embodiments are merely representative examples of the invention. Obviously, the invention is not limited to the above embodiments and many variations are possible. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the invention should be considered within the scope of protection of this invention.

[0040] Furthermore, the description of the above technical solutions is exemplary, and this specification may be embodied in different forms and should not be construed as limiting it to the technical solutions set forth herein. Rather, providing these descriptions will ensure that the disclosure of this invention is thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Moreover, the technical solutions of this invention are defined only by the scope of the claims. Features of various embodiments of the invention may be combined or spliced ​​together in part or in whole, and may be implemented in various different configurations as will be fully understood by those skilled in the art. Embodiments of the invention may be implemented independently of each other or may be implemented together in an interdependent relationship.

[0041] For those skilled in the art, without departing from the concept of this invention, several simple deductions or substitutions can be made, and all of these should be considered to fall within the protection scope of this invention.

Claims

1. A pipeline leak detection method based on negative pressure induction and nitrogen concentration change, characterized in that, Includes the following steps: S1) On the pipeline under negative pressure during operation, a first detection point P1 and a second detection point P2 are set along the axial direction. Both detection points are equipped with nitrogen concentration sensor, oxygen concentration sensor, pressure sensor and temperature and humidity sensor. S2) Real-time acquisition of nitrogen concentration, oxygen concentration, pressure, temperature and humidity data at the first detection point P1 and the second detection point P2; calculation of water vapor partial pressure based on temperature and humidity data; conversion of the original volume fractions of nitrogen and oxygen into dry basis standard conditions concentration. S3) Calculate the nitrogen dry basis standard condition concentration difference ΔN, oxygen dry basis standard condition concentration difference ΔO, and pressure difference ΔP between the first detection point P1 and the second detection point P2 at the same time. S4) The nitrogen concentration difference ΔN, oxygen concentration difference ΔO, and pressure difference ΔP are respectively compared with the preset nitrogen threshold ε. N Oxygen threshold ε O Pressure threshold ε P The comparison is performed, and if any difference exceeds the corresponding threshold, it is determined that there is a leak in the pipeline.

2. The pipeline leak detection method based on negative pressure induction and nitrogen concentration change as described in claim 1, characterized in that: In step S2), the water vapor partial pressure P H2O Calculate using the following formula: P H2O =H×6.112×exp((17.62×T) / (243.12+T)) 100, where H is the relative humidity and T is the temperature.

3. The pipeline leak detection method based on negative pressure induction and nitrogen concentration change as described in claim 2, characterized in that: Conversion of nitrogen dry basis standard condition concentration C std =C meas ×(P meas -P H2O ) / P std ×(T meas +273.15) / T std In the formula, C meas P represents the nitrogen concentration detected at the first detection point P1 and the second detection point P2. meas T represents the absolute pressure at the first detection point P1 and the second detection point P2. meas P represents the temperature detected at the first detection point P1 and the second detection point P2. std T is the standard atmospheric pressure. std The standard state temperature is 273.15 K. Conversion of oxygen dry basis standard condition concentration O std =O meas ×(P meas -P H2O ) / P std ×(T meas +273.15) / T std In the formula, O meas P represents the oxygen concentration detected at the first detection point P1 and the second detection point P2. meas T represents the absolute pressure at the first detection point P1 and the second detection point P2. meas P represents the temperature detected at the first detection point P1 and the second detection point P2. std T is the standard atmospheric pressure. std The standard temperature is 273.15 K.

4. The pipeline leak detection method based on negative pressure induction and nitrogen concentration change as described in claim 1, characterized in that: After a leak is detected, the leakage amount is estimated based on the rate of change of nitrogen and oxygen concentrations and the rate of change of pressure, combined with calibration coefficients.

5. The pipeline leak detection method based on negative pressure induction and nitrogen concentration change as described in claim 1, characterized in that: The formula for estimating air leakage is: Q leak =α N ×ΔN / Δt+α O ×ΔO / Δt+β×ΔP / Δt, where α N α is the contribution factor of the change in nitrogen dry-basis standard condition concentration to the leakage rate. O α is the contribution coefficient of the change in oxygen dry-basis standard condition concentration, β is the contribution coefficient of the pressure change, Δt is the sampling interval, and α is the contribution coefficient. N α O β is obtained by calibration experiments under leak-free conditions, using the leakage or controllable leakage of a known orifice size to compare with the actual measured rate of concentration change or pressure change.

6. The pipeline leak detection method based on negative pressure induction and nitrogen concentration change as described in claim 4, characterized in that: The system classifies leaks based on their magnitude and triggers on-site alarms or uploads data to a remote monitoring platform via a communication module, enabling automatic online response.

7. The pipeline leak detection method based on negative pressure induction and nitrogen concentration change as described in claim 6, characterized in that: Set a first threshold Q1 and a second threshold Q2, where Q1<Q2, if the gas leakage amount Q leak ≤Q1, it is determined that there is no obvious leakage; if Q1<Q leak <Q2, it is determined that there is a slight leakage; if Q leak ≥Q2, it is determined that there is a serious leakage.

8. The pipeline leak detection method based on negative pressure induction and nitrogen concentration change as described in claim 1, characterized in that: In step S1), the nitrogen concentration sensor has a range of 0 to 10% and an accuracy of ±0.01%, the oxygen concentration sensor has a range of 0 to 5% and an accuracy of ±0.005%, the pressure sensor has a range of -10 kPa to +10 kPa and an accuracy of ±10 Pa, and the temperature and humidity sensor has a temperature range of -20℃ to +60℃ and an accuracy of ±0.5℃, and a humidity range of 0 to 100% and an accuracy of ±2%RH.

9. A pipeline leak detection device based on negative pressure induction and nitrogen concentration change, characterized in that: The pipeline leak detection method based on negative pressure induction and nitrogen concentration change as described in any one of claims 1 to 8 includes: The first detection unit and the second detection unit are respectively installed at the first detection point P1 and the second detection point P2 along the pipeline axis. Each detection unit includes a nitrogen concentration sensor, an oxygen concentration sensor, a pressure sensor and a temperature and humidity sensor. The data acquisition and preprocessing module is connected to each sensor and is used to collect nitrogen concentration, oxygen concentration, pressure, temperature and humidity data at the first detection point P1 and the second detection point P2 in real time. It calculates the water vapor partial pressure based on the temperature and humidity data and converts the original concentrations of nitrogen and oxygen into dry basis standard conditions. The difference calculation module is used to calculate the nitrogen dry basis standard condition concentration difference ΔN, the oxygen dry basis standard condition concentration difference ΔO, and the pressure difference ΔP between the first detection point P1 and the second detection point P2 at the same time. The leakage detection module is used to compare ΔN, ΔO, and ΔP with a preset nitrogen threshold ε. N Oxygen threshold ε O Pressure threshold ε P The comparison is performed, and if any difference exceeds the corresponding threshold, it is determined that there is a leak in the pipeline.

10. The pipeline leak detection device based on negative pressure induction and nitrogen concentration change as described in claim 9, characterized in that: It also includes a leakage estimation module, which estimates the leakage amount based on the rate of change of concentration and the rate of change of pressure, combined with the contribution coefficient, after a leak is detected.

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